Grains containing fats and oils have been dried by microwave heating followed by steps to remove husks and to extract oils, as indicated in U.S. Pat. No. 4,464,402, Aug. 7, 1984 (Gannon). The use of microwave energy to heat an extractant medium has also been investigated by Ganzler & Salgo, 1987, Z. Lebensm Unters Forsch 184: 274-276. In the latter type of application, most of the microwave energy is absorbed by the extractant subsequently resulting in the heating of the extractant; accordingly, very little energy reaches the inner parts of the material to be extracted.
Plant material has been exposed to microwave energy in an air stream to produce headspace-like samples of volatile material as documented by Craveiro et al., 1989, Flavour and Fragrance Journal 4: 43-44. No documentation has been compiled in terms of the ability to generate volatiles in a dynamic mode, such as those produced by purge and trap methods, and further no novel apparatus therefor has been set forth.
Canadian Pat. No. 987,993 issued to Heitkamp et al., describes a microwave-induced migration of flavours and aromas to the surface of materials, such as tobacco or tea, in the presence of moisture and optionally, a solvent. In U.S. Pat. No. 5,002,784, Pare et al., teach that biological materials containing microwave absorbing substances, which are subjected to microwave radiation while in contact with an extractant microwave transparent or partial transparent, results in differential heating of the material to be extracted. The latter effects a disruption of the inner glandular and vascular systems of the material and causes a very rapid selective extraction of a variety of natural products.